1. Field of the Invention
The present invention relates to a photographic film cartridge with a bar code disc, and a bar code reader for use therewith. More particularly, the present invention relates to an apparatus for reading a bar code recorded on a bar code disc while the bar code disc rotates with the cartridge spool in a camera.
2. Description of the Related Art
There is known a photographic film cartridge of the type wherein the leader of the photographic film is advanced out of the cartridge shell by the rotation of the cartridge spool. U.S. Pat. No. 5,049,912 describes an improved version of the photographic film cartridge of this type and a camera that uses it. This photographic film cartridge has a bar code disc mounted on the cartridge spool, the bar code disc being provided with written information specific to the cartridge, such as the sensitivity of the loaded film and the number of frames capable of being photographed. The camera has a bar code reader for reading a bar code recorded on the disc while the cartridge spool rotates. If a bar code is represented by a plurality of bars of different widths, it is necessary to rotate the bar code disc at a constant angular velocity within the camera and to discriminate the bar widths based upon the time period of detecting each bar. If the rotation speed of the cartridge spool is unstable, it becomes necessary to use a highly precise rotary encoder coupled to the bar code disc and to check the film advance amount from a pulse generated by the encoder per unit of rotational angle, each unit comprising a very small angle.
The rotation speed of a motor for driving a take-up spool for winding up a photographic film within the camera changes with the environmental temperature and the power consumption of a camera battery. Even if the rotation speed of the motor is constant, the film advance speed changes with the diameter of the film roll wound about the take-up spool. A change in the film advance speed results in a change in the angular velocity of the cartridge spool rotating with the advance of the photographic film. It is therefore very difficult in practice to rotate the cartridge spool at a constant angular velocity. Use of a precise rotary encoder merely for reading a bar code is disadvantageous as to assembly space and cost.